The 32-year-old actress won't be the only Hollywood star on the sidelines. Orlando Bloom and Zoe Saldana will also be cheering on the ponies and players. Fellow Brits Alex Pettyfer plus Rosie Huntington-Whiteley -- she joked earlier this month that she was "obsessed" with Prince Harry -- will also be at the match, the source confirms.

The royals' A-list mingling doesn't end in Santa Barbara. Following the polo match, they'll head back to L.A. for a BAFTA reception held at the Belasco Theater, where celebs like Jennifer Lopez, Nicole Kidman, Barbra Streisand, Dana Delaney, Cat Deeley and others are expected to attend.